1. Field of the Invention
The present invention relates to aqueous paint suspensions containing a film-forming polymer. The invention also relates to an aqueous aerosol paint composition incorporating such suspensions. In particular, the invention relates to aqueous aerosol paint compositions suitable for temporary marking applications.
2. Description of the Related Art
Aerosol paint compositions comprising film-forming polymers are known in the paint industry. However, the majority of such aerosol paint compositions utilize large amounts of volatile organic solvents as carrier for the film-forming polymer. Because they are organic solvent-based, such compositions typically are compatible with, and hence can employ, hydrocarbon propellants. But aerosolized paint compositions containing large amounts of volatile organic solvents present environmental and health concerns and are therefore undesirable.
A smaller number of aerosol paint compositions utilize water as carrier for the film-forming polymer. However, including water as the solvent in aerosols generally causes foaming upon application when hydrocarbon propellants are used. Accordingly, the preferred propellant for water-based aerosols is dimethyl ether, which acts as a co-solvent when added to the aerosol paint composition. But because dimethyl ether is much more expensive than hydrocarbon propellants, such aqueous aerosol spray paint compositions are not cost efficient.
In general, paint compositions function by depositing a layer of pigment onto a substrate. The pigment is typically suspended or solubilized within a carrier fluid that volatilizes or dries after the paint composition is applied, leaving behind a hardened pigment film. Thus, the key performance characteristic of both organic solvent-based and water-based paints is to deposit a permanent film for surface protection. By contrast, a key performance characteristic of aqueous aerosol paints of the present invention is to deposit a temporary film that easily may be removed with water.
The removable aqueous aerosol paints of the present invention are very useful for temporary applications where it is desirable to have water-removable markings or to allow rain water to wash the markings out. Aqueous aerosol paints of the invention can be used as tunnel markers and as road markers. They may be used by surveyors and landscapers for ground marking or utility line identification. Aqueous aerosol paints of the invention are also very useful for marking tanks and lumber for identification purposes.
In general, pigments useful for various paint compositions consist of fine particles. However, when fine particles of pigment are dispersed in aqueous vehicles, it is often difficult to obtain stable dispersions, and various problems arise that can have a serious impact on the preparation and value of the resulting product. For example, dispersions containing pigments consisting of fine particles are often viscous and difficult to expel in an even spray pattern from an aerosol container. Moreover, when pigments of different types are used, undesirable phenomena such as uneven levelling and color separation by flocculation and precipitation can occur.